1. Field of the Invention
The present invention relates to a toner for use in developing a static charge image formed in methods for forming an image such as an electrophotographic method, electrostatic recording method, and electrostatic printing method, and also relates to a method for forming a full-color image using the toner.
2. Description of the Related Art
In recent years, in a full-color copying machine, there has been used: a method in which four photosensitive members and a belt-like transfer member are used, and static charge images formed on the respective photosensitive members are developed using cyan, magenta, yellow, and black toners, and subsequently transferred onto a transfer material conveyed between the photosensitive member and the belt-like transfer member during passing the transfer material straightly to form a full-color image; or a method in which the transfer material is wound around the surface of the transfer member by an electrostatic force or a mechanical function like a gripper, the transfer member is disposed opposite to the photosensitive member, and a step of developing and a step of transferring is carried out four times to obtain a full-color image.
Moreover, for the toner for use in the full-color copying machine, colors of the respective toners are requested to be sufficiently mixed in a step of heating/pressurizing/fixing from viewpoints of enhancement of color reproducibility or transparency of an overhead projector (OHP) image.
Therefore, as the toner for the full-color copying machine, a low molecular weight binder resin, which has a sharp melt property as compared with a toner for a general monochromatic copying machine, has been used. However, with the use of the low molecular weight binder resin, resistance to high-temperature offset sometimes drops, when the toner is molten in the step of heating/pressurizing/fixing.
Even when mold release agents such as a polyethylene wax and polypropylene wax are added to the toner in order to enhance the resistance to high-temperature offset at the time of the fixing, for the toner for full color using the low molecular weight binder resin, the binder resin is completely molten in the step of heating/pressurizing/fixing, and therefore the mold release agent does not sufficiently fulfill its effect. Therefore, it has been difficult to sufficiently reduce high-temperature offset.
In order to reduce the high-temperature offset, coating a fixing roller with an oil is also performed, but with the use of the oil, an oil streak in an image at the time of the fixing sometimes raises a problem.
To solve the problem, a toner and a method for forming an image have been proposed in which toner particles are manufactured by a suspension polymerization method, a wax is contained in the toner particles, and accordingly any fixing oil is not used (e.g., Japanese Patent Application Laid-Open Nos. 8-314300 and 8-50368).
However, when a large amount of wax is contained in the toner, concave/convex portions are easily made in the surface of the fixed image with the toner including the binder resin containing a styrene-acryl resin which is a major component. As a result, permeability of the OHP drops.
Moreover, a large number of toners have been proposed, including: a toner which shows a specific melting behavior in a nip portion of a fixing device (e.g., see Japanese Patent Application Laid-Open No. 10-39538); a toner which has a specific viscoelastic characteristic (e.g., see Japanese Patent Application Laid-Open No. 2001-75305); and a toner which contains a specific wax (e.g., see Japanese Patent Application Laid-Open Nos. 2002-14488, 2002-14489, and 2002-40712). However, with respect to either compatibility between low-temperature fixing property and resistance to high-temperature offset, or the transparency of the OHP fixed image, any sufficiently satisfactory toner has not been proposed yet.
To solve the problem, there has been a demand for a toner which realizes the compatibility between the low-temperature fixing property and resistance to offset in the step of heating/pressurizing/fixing not using any oil for preventing the high-temperature offset or using a reduced use amount of the oil, and which is superior in the transparency of the OHP fixed image.